The present invention relates to an indexing device provided in a machine tool. More particularly, the present invention relates to a turret tool rest capable of selecting a desired tool from a plurality of tools mounted at regular circumferential intervals and locating the selected tool at a machining-work position by the indexed rotation of the turret tool rest.
In a field of machine tools, it is well-known that a turret tool rest capable of mounting a number of tools is used for facilitating the automation of the machining work and an increase in the machining speed, as well as for meeting a multi-item low-volume production. For example, a turret tool rest used in an automatically operated lathe is constituted by a tool slide disposed on a lathe bed at a position opposed to a rotary spindle, a tool rest body provided on the tool slide to be movable along a given coordinate axis, and a turret supported for rotation on the tool rest body and capable of respectively mounting various tools, such as cutting tools or drills, at a plurality of angularly-indexed positions around a rotation axis. In this regard, the automatically operated lathe described herein means any turning machine tools, such as NC lathes, capable of carrying out an automatic machining or turning operation.
In the turret tool rest, after the indexing rotation of the turret is performed, it is necessary to firmly secure the turret at an indexed position on the tool rest body during the machining of a workpiece with a selected tool. Accordingly, a mutually engageable and disengageable pair of engaging elements are generally disposed between the tool rest body and the turret. By mutually engaging/disengaging (or clamping/unclamping) the pair of engaging elements, it is possible to allow the indexing rotation of the turret or to locate and secure the turret at a desired indexed position.
A coupling unit in the form of an intermeshable pair of coupling members like a claw-clutch mechanism, each having a number of claws on one axial end surface, has been known as an engaging unit formed from abovementioned pair of engaging elements. In this type of engaging unit, the clamping/unclamping operation is generally performed by linearly displacing one engaging element provided for the turret in an axial direction relative to the other engaging element provided for the tool rest body by an exclusive clamp/unclamp drive mechanism.
An example of a tool selection procedure is described below. First, after a machining work on a workpiece by one tool has completed, the tool rest body is moved together with the turret on the tool slide, so as to shift a tool backward from a machining-work position to a tool-exchangeable position. Then, the turret-side engaging element is moved to be disengaged from the tool rest body-side engaging element by the clamp/unclamp drive mechanism, and, in this condition, the turret is rotated by another rotation drive source to perform an indexing rotation, so as to select a desired tool. Next, the turret-side engaging element is engaged with the tool rest body-side engaging element by the operation of the clamp/unclamp drive mechanism, so as to securely hold the selected tool at an indexed position. In this condition, the tool rest body is moved together with the turret on the tool slide, so as to feed the tool from the tool-exchangeable position to the machining-work position.
An automatically operated lathe, such as an NC lathe, includes a plurality of drive sources for respectively driving different objectives, such as a drive source for rotating a spindle, respective axial drive sources for feeding a tool, a drive source for opening/closing a spindle chuck, and so on. For these drive sources, servomotors have been generally used, particularly in portions (such as a spindle or a tool-feed) requiring a high-speed and high-precision response. In recent years, servomotors also tend to be used in portions wherein hydraulic or pneumatic actuators have been conventionally used, such as the chuck opening/closing drive source or the turret rotation drive source in the turret tool rest described above, because of the advantages of environmental sanitation and operational reliability in the servomotors.
In the above-described clamp/unclamp drive mechanism for the turret tool rest, however, electric-motorization has been delayed and hydraulic or pneumatic actuators are still used in most cases, due to, e.g., the fact that a required operation is a simple one for merely slightly displacing one of engaging elements in an axial direction. The hydraulic or pneumatic actuators generally possess problems such as the deterioration of working environment due to noise or atmospheric pollution, the rise of equipment cost, the enlargement of machine size, low precision of response, and so on. Particularly, when a hydraulic cylinder is used as the clamp/unclamp drive mechanism, the operation speed easily varies due to the change in temperature of hydraulic fluid, so that the time required for clamping/unclamping the engaging elements fluctuates, which results in difficulties in the stable control of sequential turret-indexing operations. Also, since the hydraulic cylinder itself constitutes a considerable heat source and a thermal expansion of peripheral machine components is caused which results in difficulties in obtaining a stable machining accuracy. Therefore, the electric-motorization of the clamp/unclamp drive mechanism of the turret tool rest has been also desired.
On the other hand, in the turret tool rest with an electrically motorized drive source, a servomotor as a turret rotation drive source is provided on the tool rest body, and, in the case where not only stationary tools such as a cutting tool but also rotary tools such as a drill can be mounted, another servomotor is also provided on the tool rest body for the rotary tools. Moreover, if a further servomotor is provided as a clamp/unclamp drive source on the tool rest body in response to the demand for the electric-motorization of the clamp/unclamp drive mechanism, a weight of the tool rest body, as one of moving elements along a given coordinate axis on the lathe bed, unduly increases, which may result in the lowering of response accuracy, and may cause the problems of the enlargement of entire machine dimensions, the rise of production and operating cost, and so on.
Accordingly, an object of the present invention is to provide a turret tool rest in which the electrical motorization of a clamp/unclamp drive mechanism capable of securely holding and releasing a turret at an indexed position on a tool rest body can be performed without incorporating an additional motor, so that several effects, such as the mitigation of noise or atmospheric pollution, the saving of energy consumption, the improvement of response accuracy, the reduction of production and operating cost, and so on, can be obtained, and that the further reduction of dimensions of a machine tool and the further improvement of performance thereof can be facilitated.
To achieve the above object, the present invention provides a turret tool rest, comprising a base; a tool rest body movably provided on the base; a turret rotatably supported on the tool rest body, the turret permitting desired tools to be individually mounted at predetermined angularly-indexed positions; an electric motor for rotationally driving the turret; a clutch unit arranged between the turret and the electric motor, the clutch unit operatively connecting the turret with the electric motor in a releasable manner; a drive mechanism for operating the clutch unit; an engaging unit arranged between the tool rest body and the turret, the engaging unit engaging the turret with the tool rest body in a disengageable manner; and a power transmission device arranged between the electric motor and the engaging unit, the power transmission device transmitting an output of the electric motor to the engaging unit so as to operate the engaging unit; wherein, when the engaging unit is in a disengaged state, the clutch unit is set in a connecting state and an indexing rotation of the turret is caused by the electric motor, and when the clutch unit is in a releasing state, the engaging unit is set in an engaged state and the turret is secured at an indexed position on the tool rest body.
According to a preferred aspect of the present invention, the drive mechanism includes an interlocking device for operating the clutch unit in association with a movement of the tool rest body on the base.
In this arrangement, it is preferred that the interlocking device includes a cam provided on the base and a follower member provided on the tool rest body to be slidably engaged at one end with the cam and operatively connected at another end with the clutch unit, the clutch unit being operated due to a rotation of the follower member generated by the movement of the tool rest body on the base.
It is also preferred that the clutch unit includes a clutch shaft coupled to an output shaft of the electric motor for rotation and a rotatable annular clutch member arranged coaxially with the clutch shaft and connected to the turret, the annular clutch member being engageable and disengageable with the clutch shaft.
Preferably, the turret includes an index gear fixedly provided and arranged coaxially with the turret, and the annular clutch member is provided on an outer periphery with a toothed portion for meshing with the index gear.
Preferably, the clutch shaft is provided on an outer periphery thereof with a meshing portion, and the annular clutch member is attached to the clutch shaft in an axially movable and rotatable manner, the annular clutch member being provided on one axial end thereof with a corresponding meshable portion for meshing with the meshing portion in a disengageable manner.
It is advantageous to further comprise a sensing unit for sensing an inadequate engagement of the clutch shaft with the annular clutch member.
It is desirable to further comprise a power absorbing mechanism for absorbing an output of the drive mechanism when the inadequate engagement of the clutch shaft with the annular clutch member is generated.
It is advantageous to further comprise a stop member for being engaged with the annular clutch member to stop a rotation of the annular clutch member when the annular clutch member is disengaged from the clutch shaft.
Preferably, the stop member is arranged to stop the rotation of the annular clutch member before the annular clutch member is completely disengaged from the clutch shaft.
It is advantageous to further comprise a sensing unit for sensing an inadequate engagement of the stop member with the annular clutch member.
It is desirable to further comprise a power absorbing mechanism for absorbing an output of the drive mechanism when the inadequate engagement of the stop member with the annular clutch member is generated.
The engaging unit may include an immovable-side engaging element provided on the tool rest body and a movable-side engaging element provided on the turret, and the power transmission device may move the movable-side engaging element between an engaged position for engagement with the immovable-side engaging element to stop a rotation of the turret and a disengaged position for disengagement from the immovable-side engaging element to permit the rotation of the turret.
The power transmission device may include a feed screw arrangement provided on the turret and a gear train for connecting an output shaft of the electric motor to a rotating element of the feed screw arrangement.
The rotating element of the feed screw arrangement may be arranged to rotate synchronously with the turret in an identical direction during the indexing rotation of the turret.
The present invention also provides an automatically operated lathe including a turret tool rest, comprising a lathe bed; a base provided on the lathe bed; a tool rest body movably provided on the base; a turret rotatably supported on the tool rest body, the turret permitting desired tools to be individually mounted at predetermined angularly-indexed positions; an electric motor for rotationally driving the turret; a clutch unit arranged between the turret and the electric motor, the clutch unit operatively connecting the turret with the electric motor in a releasable manner; a drive mechanism for operating the clutch unit in association with a movement of the tool rest body on the base; an engaging unit arranged between the tool rest body and the turret, the engaging unit engaging the turret with the tool rest body in a disengageable manner; and a power transmission device arranged between the electric motor and the engaging unit, the power transmission device transmitting an output of the electric motor to the engaging unit so as to operate the engaging unit; wherein, when the engaging unit is in a disengaged state, the clutch unit is set in a connecting state and an indexing rotation of the turret is caused by the electric motor, and when the clutch unit is in a releasing state, the engaging unit is set in an engaged state and the turret is secured at an indexed position on the tool rest body.